Stroke occurs when focal cerebral ischemia is severe, prolonged or both. Brain tissue where cerebral blood flow is under 17 mls/min/100 g dies within a minute or two (core), tissue with blood flow 18-50 mls/min/100 g is viable for up to 30 minutes, and tissue with higher blood flow is potentially viable indefinitely (penumbra). Any procedure which increases perfusion to within the penumbral range may salvage brain tissue indefinitely. Cerebral perfusion augmentation early in the ischemic event has been shown to reduce infarct size and improve outcome from stroke in animal models. There are numerous methods for attempting to increase cerebral perfusion but the hemodynamic effect on actual cerebral perfusion has been inconsistent, and several of them have increased the risk of cerebral hemorrhage.
None of the existing techniques has yet been shown to improve outcome from stroke in human randomized trials. Moreover, mechanical methods designed to augment perfusion are invasive procedures requiring trained personnel, and they cannot be administered early in the course of the ischemia. Improvements over conventional therapies are thus desirable. In particular what is needed is a therapy that is non-invasive and easily administrable by first responders early in the course of ischemia.